Increasing numbers of people in the UK chronically infected with the hepatitis C virus are being admitted to hospital with potentially fatal liver disease, according to the NHS's public health watchdog.

New diagnoses are also rising sharply, although this is thought to be mainly down to more testing following huge publicity campaigns, especially among injecting drug users. One use of unsterilised needles or syringes can be enough for an infection to be passed on.

The disease can take decades to manifest itself, although it is thought up to one in five people recover naturally in the first six months after contact. Symptoms include fatigue, weight loss, nausea, flu-like symptoms, problems concentrating, abdominal pain and jaundice.

About 216,000 people in the UK are now thought to be infected, according to the Health Protection Agency (HPA). Thousands of people were also infected accidentally through contaminated blood products in the 1970s and 1980s. Others at risk include those from countries, including some in south Asia, where the virus is endemic and unsterilised medical and dental equipment is commonly used.

New diagnoses reported in England rose from 7,892 in 2010 to 9,908 in 2011. In the UK hospital admissions for end-stage liver disease related to hepatitis C rose from 612 in 1998 to 1,979 in 2010. Deaths rose from 98 in 1996 to 323 in 2010. Registrations for liver transplants after hepatitis C-related cirrhosis rose from 45 in 1996 to 101 in 2011. The virus causes inflammation of the liver and, if left untreated, can result in chronic liver disease, liver failure, or even death. Many people are unaware they have the disease at first because they have no symptoms. It is only when the liver becomes seriously damaged that symptoms occur and people report to their doctor.

Helen Harris, a hepatitis expert at the HPA, said: "Many of the 216,000 people who are chronically infected with the virus are unaware of their infection. Therefore, it is vital that we continue to monitor the true burden of infection to help focus public health action on getting these people diagnosed and into treatment."

She said hepatitis C infection was usually treatable if caught early enough. "We must therefore redouble our efforts and continue to develop new schemes to raise awareness in at-risk communities and ensure that individuals who may have been exposed to the virus are tested, diagnosed and treated early, before they become seriously ill."

Harris added: "It's very encouraging that new drugs are now available that can help clear the most difficult-to-treat strain of the virus in most people." She said that between 2006 and 2011, an estimated 27,500 people with chronic hepatitis C in England had been treated with combination therapy, but more people needed to access it. "It's important that hepatitis C provision continues to be a priority for the NHS, particularly for those marginalised groups of society who are most affected by the epidemic."